The present invention relates to charcoal production and in particular to a method for converting woody biomass feed material into useful charcoal briquettes.
Biomass is comprised mainly of cellulose, hemi cellulose and lignin. A typical woody biomass may contain 40-50% cellulose, 25-35% hemi cellulose, and 15-18% lignin. Typical yields from a slow pyrolysis machine are 30% charcoal containing 70% plus carbon, 35% non-condensable gases containing hydrogen, methane, carbon mono oxide, carbon dioxide primarily, and 35% pyrolysis oil, also known as bio oil or bio crude, consisting tar, aldehydes, formic acid, acetic acid, water, esters, phenols, sugar derivatives, lignins. Such typical slow pyrolysis machine yields oil and charcoal in nearly equal portions. Slow pyrolysis involves heating of dried biomass (<8% moisture) in an oxygen free environment at 450-500 degrees centigrade in heated auger tubes. The process involves thermo chemical conversion of solid biomass to a liquid product, bio oil, and solid material, charcoal. Non-condensable gases are utilized to heat the incoming wet biomass material, thus creating a closed loop system.
Convention slow pyrolysis process yields bio oil that has the following properties:
Chemical formula: CH1.3O0.47 
Flash point: 80 deg C.
pH=2.5
Sp Gr.=1.2
Moisture content: 20-25%
Heating value=7,522 btu/lb (17.5 mj/kg)
Viscosity=60-100 cp
and
Elemental analysis:
C=55-60%
H=5-8%
O=28-40%
N=0.06%
Rotary dryers are commonly used to dry biomass. There are several variations of rotary dryers, but the most widely-used is the directly heated single-pass rotary dryer. The directly heated single-pass rotary dryer uses hot gases contacting the biomass material inside a rotating drum. The rotation of the drum, with the aid of flights, lifts the solids in the dryer so they tumble through the hot gas, promoting better heat and mass transfer. The biomass and hot air normally flow co-currently through the dryer so the hottest gases come in contact with the wettest material. The exhaust gases leaving the dryer may pass through a cyclone, multicyclone, baghouse filter, scrubber or electrostatic precipitator (ESP) to remove any fine material entrained in the air. An ID fan may or may not be required depending on the dryer configuration. If an ID fan is needed, it is usually placed after the emissions control equipment to reduce erosion of the fan, but may also be placed before the first cyclone to provide the pressure drop through downstream equipment. The inlet gas temperature to rotary biomass dryers can vary from 450°-2,000° F. (232°-1,093° C.). Outlet temperatures from rotary dryers vary from 160° to 230° F. (71°-110° C.), with most of the dryers having outlet temperatures higher than 220° F. (104° C.) to prevent condensation of acids and resins. Retention times in the dryer can be less than a minute. While known dryers generally perform adequately, they consume significant energy increasing the cost of processing the biomass material.
Further, known systems have difficulty processing wet biomass material, may produce unwanted oil, exhaust process gas, and lack efficiency.